Telephone circuit



Aug. 18, 1942 G. l.. KNITTLE ETAL TELEPHONE CIRCUIT Filed Junev 7, 1941 E Opel ato/.s Col-d CLV-cuit MMM) M ATTORNEY Patente-cl Aug. 18, 1942 UNITED STATES PATENT OFFICE TELEPHONE CIRCUIT Rank, Berwyn,

tion of New York Ill.,

Application June '7, 1941, Serial No. 397,038

Claims.

This invention relates to telephone circuits and systems, and more particularly to arrangements for improving such circuits and systems so that signaling between the subscriber and the telephone operator may be accomplished more efficiently, especially in cases where the subscribers loop is a long one, or is formed of small gauge Wire.

As is well known, the circuit of the A operators position includes a battery, usually of 24 volts, a repeating coil, and a supervisory relay, the latter relay being energized by current from the battery when the subscribers station circuit is connected to the A operators cord circuit. This supervisory relay is of the usual single inductive winding type (with a bridged non-inductive winding) and it includes a core of iron which has some residual magnetism after the relay winding has become deenergized. For toll switching operations the subscribers station circuit is also connected to the B operators trunk circuit which usually includes a battery of higher voltage of, for example, 48 volts. This battery voltage is also applied to the winding of the supervisory relay in the A operators cord circuit during the interval when both the cord and trunk circuits are simultaneously connected to the subscribers station circuit. The two voltages are poled with respect to the supervisory relay winding so as to oppose each other, and hence the larger voltage from the B operators trunk circuit will dominate and therefore reverse the previous magnetization of the relay core. In other words, the application of the higher voltage to the supervisory relay winding during toll switching operations produces a net effect in the magnetic structure of the supervisory relay which is opposite to that caused alone by the lower voltage of the A operators circuit. And after the cord and trunk circuits become disconnected from each other, the relay core will have residual magnetism poled opposite to its former polarity.

It has been discovered that because the core of the supervisory relay of the A operators cord circuit obtains a reverse soak when the B operators trunk circuit, (also known as a toll switching trunk) is plugged into the multiple jack of the subscribers circuit, more current is required to operate the supervisory relay soon thereafter than under ordinary conditions. Because of this difficulty, should the A operators cord circuit involved in the toll call be soon afterwards used to answer a subsequent call from a subscriber, the supervisory relay may not operate satisfactorily. In that eventthe operator may disconnect her circuit from the subscribers line while the subscriber remains on the line. This adverse condition has become especially troublesome on the longer subscribers loops as well as on loops of smaller gauge Wire which are rapidly coming into more extensive use in telephone systems.

It is an object of this invention to eliminate the adverse conditions just referred to by shunting the higher voltage supplied by the B operators trunk circuit from the winding of the supervisory relay of the A operators cord circuit.

It is another object of this invention to arrange the circuit of the supervisory relay so that only the voltage in the A operators cord circuit may be applied to its winding. This may be accomplished, for example, by adding elements to the circuit which will freely transmit the current of the cord circuit battery to the winding of the relay, and will also by-pass current from the higher voltage battery of the B operators trunk circuit around the relay winding. Y

This invention will be better understood from the detailed description hereinafter following when read in connection with the accompanying drawing showing one embodiment of the invention merely for the purpose of illustration.

Referring to the drawing, the local subscribers circuit designated S is sliown at the right, this circuit including the usual induction coils Y1, a telephone receiver R, a telephone transmitter T, a ringer D, switch hook I-I and the condenser C1. The telephone set S may be connected in the usual way over the subscribers loop to the tip and ring sides of the jack J 1 at the central oflice as shown. The A operators cord circuit includes, among other things, the usual repeating coils Y2 and Ys, the battery B1, ordinarily of around 24 volts, the supervisory relay W1, the inductive winding of which is shunted by a non-inductive resistor X1, and the plug P1 as shown. The B operators trunk circuit for toll switching operations includes the usual repeating coils Y.; and Ys, the condensers C2 and C3, the relay W2 and the grounded battery B2, which is ordinarily of about 48 volts, a Voltage which is higher than that of the battery B1 of the A operators cord circuit. The B operators trunk circuit terminates in a plug P2, which may engage the multiple jack J2 associated with the local subscribers circuit S. Y

The A operators cord circuit also includes two rectiiiers or other non-linear devices designated Z1 and Z2. The rectilier Z2 is so poled that it will freely transmit current from battery B1 through the winding of the supervisory relay W1, while at the same time opposing any flow the A operator as, for example, by removing the receiver R from the switch hook H, the relay W3 will immediately operate, current flowing from the battery B3 through the right-hand winding of relay W3, the lower armature and back contact of the cut-off relay W4, the lower conductor of the subscribers loop, the transmitter T, the

switchhook H, the left-hand winding of the in- A duction coil Y1, the upper conductor of the subscribers loop, the upper armature and back contact of the relay W4, the left-hand winding of relay W3' and ground. The operation of the relay w3 will illuminate 111e lamp L1 beeause of the ilow of current from the battery B4 to that lamp when the armature of relay W3 closes its contact. The lamp L1v will attract the A operators attentionA and she will then insert her plug P1 into the subscribers jack J1. After this connection is established the lamp-L2r will remain extinguished' although current flows from battery B5, through lamp L2, resistor X2, the sleeve contacts of plug P1Y and jack J1, the winding of the cut-off relay W4V andV ground. The lamp L2 remains extinguished; because of the presence of resistance X3 in the lamp L2 circuit. The relay W1 will, however, operate and release the relay W'a. The release of the relay W3 will extinguish the lamp L1. The relay W1 will also operate, current for which is supplied by battery B1 over a circuit which includes the right-hand winding of the repeating coil Ya, Vthe rectifier Z2, the winding of relay W1, the ring contacts of plug P1 and jack J1, the` lower conductor of the subscribers loop, the transmitter T, the switchhook H, the lefthand windingof induction coil Y1, the upper conductor of the subscribers loop, the tip conductors of jack J1 and plug P1, the right-hand winding of repeating coil Y2 and ground. The relay W1 will remain operated as long as the plug P1 and jack .T1 are in engagement and the subscriber keeps his receiver R off the switchhook H. The battery B1 will now be supplying current through the winding of relay W1 to the transmitter T at the subscribers set S to facilitate the transmission of speech currents.

Assume now that the local subscriber at station S informs the operator of his desire to make a toll call. The A operator will then establish the connection to the toll operator who will then instruct the B operator to insert plug P2 into the subscribers multiple jack J2. When this happens, both the A operators cord circuit connected to plug Pi. and the B operators trunk circuit connected to plug P2 are simultaneously connected' to the subscribers set S. Current then ows from battery B2 not through the winding of relay W1, asin prior art schemes, but through therectier Z1 instead. The circuit carrying the current of battery B2 includes the winding of relay W2', the right-hand winding of the repeating coil Ys.. the ring contacts of plug P2 and jack J2, the ring contacts of jack J1 and plug P1, the rectifier Z1, the right-hand winding of repeating coil Ys, battery B1 and ground.

It will be observed that when the circuits of the A cord and the B trunk are both connected to the subscribers set S, the current from battery B2 will traverse the rectifier Z1 and, because of the polarity of the rectifier Z2, will be unable to traverse the winding of the relay W1. Were the rectiers Z1 and Z2 omitted, the greater voltage of battery B2 would overcome the smaller voltage of battery B1 when applied simultaneously to the winding of the supervisory relay W1. Hence the core of the relay W1 would be so magnetized as to be unable to operate satisfactorily when the A cord is subsequently connected to another subscriber over a long loop.

The application of two opposing voltages, such as those of batteries B1 and B2, to the winding Y of relay W1 has. been especially troublesome heretofore where the subscribers loops approach the maximurnresistance of around 750 ohms, or when the newer types of loops of smaller gauge wire were installed. The supervisory relay of the telephone plant is not adaptable for adjustment to operatey satisfactorily with loops of higher resistance under the conditions hereinabove referred to. By restricting the voltage applied to the relay winding W1 to that of the local battery B1, it is unnecessary to undergo the expense of replacing existing supervisory relays. The circuit of this invention will allow the supervisory relay to respond accurately to every movement of the svvitchhook H with loops of higher resistance.

It will be apparent that when the A operator removes her plug P1 from jack.J1 the supervisory relay W1 will then release. When this happens thev lamp L2 will remain extinguished. The relay W1 will operate only in response to current from battery B1.

I-t has been pointedV out that lamp L2 remains extinguished whenplug P1 engages jack J1 to connect the subscribers set S to the A op'erators cord circuit. In prior arrangements which did' not include devices Z1 and Z2, the addition of the B operators trunk circuit caused current from battery B2 to flow through the winding of relay W1 and retain relay W1 in operated condition. Consequently lamp L2 remained extinguished and the A operator was later signaled to disconnect herfplug P1 from jack J1 over the other end of the A oper'ators cordV circuit (not shown).

In the circuit including the devices Z1 and Z2, however, the addition of the B trunk circuit to that of the A cord circuity and the subscribers set S causes the relay W1 to release because current is no longer able to traverse its winding due to the presence of device Z2. Hence, the lamp L2 will become illuminated instantly and promptly notify the A operator to remove her plug P1 from jack J1. The lamp L2 will of course become extinguished only after the A cord circuit is removed from jack J1.

It will thus be apparent that the inclusion of devices such as Z1 and Z2 automatically gives the A operator a prompt signal to disconnect her circuit from the subscribers line. No supervision from other operators is required to effectuate this signaling operation. This is an important feature of this invention.

Although two rectiers or non-linear devicesk such as Z1 and Z2 have been described as a composite structure to be used in practising this invention, it will be understood that the shunt device Z1 may be employed without the series device Z2, and that the series device Z2 may be employed without the shunt device Z1. If but one device is used, there will be a substantial improvement observed over prior art schemes operating without such devices, but the non-linear device will have to be of relatively large physical dimensions, so as to obtain satisfactory characteristics. Such large devices are unfeasible and impractical for insertion in available switchboard space. But lf two devices such as Zi and Z2 are used together, as shown and described, the two devices so used will each be relatively small and inexpensive and they will operate much more effectively than will one such device alone.

It will be understood that the repeating coils Y2 and Ys may be one and the same repeating coil and that repeating coils Yi and Y5 may also be one and the same repeating coil.

While this invention has been shown and described in certain particular arrangements merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

l. In a telephone system, an A operators cord circuit including a battery and a relay, a B operators trunk circuit including a battery of higher voltage, a circuit interconnecting the A operators circuit to the B operators circuit, and rectifying apparatus connected to the winding of said relay and poled so as to permit the transmission of current from the battery of the A operators circuit through the relay Winding while substantially suppressing the flow of current from the battery of the B operators circuit through the relay winding.

2. In a telephone system, the combination of a subscribers circuit, a first trunk circuit, a second trunk circuit, rst and second batteries connected in said first and second trunk circuits, respectively, a circuit interconnecting the rst trunk circuit with the subscribers circuit, the latter circuit including a rectifier so poled as to permit signaling between the interconnected circuits, a relay the Winding of which shunts Said rectifier, a second rectifier connected in series with the winding oi' said relay, a circuit connecting the second trunk circuit to the interconnected circuit, the second rectier being so poled as to oppose the flow of current from the second battery through the relay Winding of current.

3. In a telephone system, the combination of a rst trunk circuit, a second trunk circuit, a subscribers set, rst and second batteries of different voltages, a relay which is connected along with said first battery in the first trunk circuit, the second battery being connected to the second trunk circuit, and means to permit current from the first battery to flow substantially freely through said relay winding while opposing the flow of current from the battery of the second trunk circuit through said relay winding when the two trunk circuits are connected to each other through the circuit of the subscribers set.

4. In a signaling system, the combination of a first circuit which is supplied with voltage of a predetermined magnitude, a second circuit which is supplied with voltage of a higher predetermined magnitude, a relay connected to the rst circuit, and means to prevent the magnetization of the core of said relay by the voltage of higher predetermined magnitude when said rst and second circuits are connected to each other, said means including a non-linear device which is connected in series with the winding of said relay so that the voltage supplied to said rst circuit will traverse the winding oi said relay, said non-linear device being poled so that the voltage of the second circuit cannot be applied to the winding of said relay.

5. In an electrical system, the combination of a relay having a core which has a substantial residual magnetic effect after it has been energized, two sources of voltage Which are connected to the relay Winding so as to produce mutually opposing voltage effects on said relay winding, and means to eliminate the voltage eiect of one of said sources so as to avoid any residual magnetic effect in said core in response to said latter voltage effect, said means including a rectier arrangement serially interconnecting the latter source of voltage and the relay Winding and so poled as to prevent the latter voltage eiiect from magnetizing the relay core, said rectier arrangement permitting the other voltage effect to energize the relay core.

GALE LEONARD KNITTLE. PAUL JONES RANK. 

